*Predicted CO2 emissions will kill reefs by end of century

*Destruction would spread throughout coastal ecosystem

By Michael Kahn

LONDON, July 6 (Reuters) - Increasingly acidic oceans and warming water temperatures due to carbon dioxide emissions could kill off the world's ocean reefs by the end of this century, scientists warned on Monday.

The experts told a meeting in London the predicted pace of emissions means a level of 450 parts per million of carbon dioxide (CO2) in the atmosphere will be reached by 2050, putting corals on a path to extinction in the following decades.

The two dozen coral reef specialists and climate change exerts represented universities, government research offices and the Intergovernmental Panel on Climate Change.

"The kitchen is on fire and it's spreading around the house," Alex Rogers of the Zoological Society of London and the International Programme on the State of the Ocean, said in a statement.

"If we act quickly and decisively we may be able to put it out before the damage becomes irreversible."

Oceans absorb large amounts of CO2 emitted by the burning of fossil fuels. But scientists say the oceans are acidifying as they absorb more carbon, disrupting the process of calcification used by sea creatures to build shells as well as coral reefs.

Researchers around the world have been urging governments to take more account of such threats to the oceans in a new U.N. treaty on fighting global warming due to be agreed in Copenhagen in December.

Coral reefs -- delicate undersea structures resembling rocky gardens made by tiny animals called coral polyps -- are important nurseries and shelters for fish and other sea life.

They also protect coastlines, provide a critical source of food for millions of people, attract tourists and are potential storehouse of medicines for cancer and other diseases.

PATH TO MAJOR DEGRADATION

"If CO2 is allowed to reach 450 ppm, as is currently widely regarded as being the most optimistic threshold target for world leaders to agree at Copenhagen, we will have put the world's reefs on a path to major degradation and ultimate extinction," John Veron, the former chief scientist of the Australian Institute of Marine Science, told the meeting.

"Such a catastrophe poses a dire threat to the future wellbeing of all humanity."

The scientists agreed that governments should strive for a level of 320 parts per million of carbon dioxide, saying 360 was a breaking point for reefs to survive.

At the current level of 387 parts per million of carbon dioxide, reefs are in serious decline, they said. This will have a future knock-effect that threatens other marine and coastal ecosystems.

Coral covers about 400,000 square km of tropical ocean floor, but needs sustained sunlight, warmer waters and high levels of carbonate to flourish.

The biggest is the Great Barrier Reef, a collection of 2,900 reefs along 2,100 km of Australia's north east coast in a marine park the size of Germany. (Reporting by Michael Kahn; editing by Anthony Barker)

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